1. Field of the Invention
The invention relates to a device for the projection of images in which the light is modulated by its passage through light polarization modulators that are constituted, for example, by the liquid crystal cells of a matrix-addressed liquid crystal panel. An object of the invention is a new arrangement that enables considerable improvement in the luminous efficiency of such projection devices, especially but not exclusively in the field of professional instruments.
2. Description of the Prior Art
In the standard image projectors using a matrix-addressed liquid crystal panel, each liquid crystal cell of this panel corresponds to an image element or picture element. To simplify the description, if we take the case where each image element may be at the maximum level of "white" or at the maximum level of "black", a cell affects a light that goes through it by modifying or not modifying its polarization depending on whether the cell is in the so-called "on" state or in the so-called "off" state, i.e. depending on whether or not an electrical field is applied to the liquid crystal cell.
In general, the light used is initially of the non-polarized type. This light is taken to have two components with orthogonal planes of polarization. Before it is applied to the liquid crystal panel, the light goes through a device known as a polarizer which rids it of one component with a given polarization so that only the other component with the other polarization is subjected, as the case may be, to the effect of the liquid crystal cells.
After having gone through the cells, the light may again have both types of polarization in a spatial distribution that is a function of the spatial distribution of the cells in the "on" state and in the "off" state. The display of the two states of the cells is obtained by then making the light pass through a polarization analysis means making it possible to carry out a polarization analysis and to act on at least one of the two components as a function of its polarization.
In the present case, this means of analysis enables one of the polarizations to be transmitted and the other to be absorbed, that is, it works like the above-mentioned polarizer.
It must be noted that, among the devices that come within the category of polarization analysis means, such as those defined above, we might cite devices known as polarization separators, the function of which is more specifically to separate the two differently polarized components into two beams having different directions as a function of their polarization.
It is observed that, in the working of a prior art projector such as the one described here above, before the light is made to go through the liquid crystal panel, one of the two polarizations of this light has to be absorbed. This results in a 50% loss of light, to which we must add losses in transmission in the polarizer and the means of analysis.